In developing a hologram of laser pulses of light, the photographic plate used for holographic flow visualization is developed to provide the hologram. However, misalignment of the laser used to provide the laser pulse can result in no pulse being received on the photographic plate. The plate is subsequently developed to determine whether or not a pulse was received as well as to obtain the hologram. The exposure meter allows detection of these light pulses, and eliminates unnecessary development of the plate.